1. Field of the Invention
The invention relates to a cathode ray tube. More particularly, the invention relates to a shadow mask frame assembly of a cathode ray tube (CRT), in which a center part of the main frames is compressed more than corner parts in welding the shadow mask thereto.
2. Background of the Related Art
Referring to FIGS. 1 and 2, a related art CRT is shown which includes a panel 1 having a fluorescent surface 4 with fluorescent materials (i.e., red, green, and blue) coated on an inside surface thereof. A funnel 2 is welded to a rear of the panel 1 with Frit glass. An electron gun (not shown) is sealed in a neck 2a of the funnel 2. The electron gun emits, accelerates, and focuses electron beams 6 for forming three colors (i.e., red, green, and blue).
A shadow mask 3 for selecting a desired fluorescent material to illuminate is disposed adjacent to the fluorescent surface 4. A frame assembly 7 holds the shadow mask 3. Springs 8 fasten the frame assembly 7 to the panel, while stud pins 18 fixed to an inside surface of a skirt part la of the panel 1 hold the springs 8. An inner shield 9 is fastened to the frame assembly 7 and is sealed under a high vacuum. The inner shield 9 minimizes an influence of external geomagnetism during operation of the CRT.
The electron beams 6 from the electron gun (not shown) provided in the neck part 2a of the funnel 2 are projected onto the fluorescent surface 4 on the inside surface of the panel 1 by an anodic voltage applied to the CRT. The electron beams are deflected in upper, lower, left, or right directions by a deflection yoke 5 before the electron beams reach the fluorescent surface, to form an image. There are two, four, or six polar magnets 10 for controlling the paths of the electron beams 6 so that they land on the correct fluorescent material, thereby preventing poor color purity.
In fabrication of a tension type shadow mask assembly, in which tension is applied to the shadow mask 3, both ends of two main frames 7-1 are held fixed by subframes 7-2. The main frames 7-1 are then compressed, and the shadow mask 3 is welded to the main frames 7-1. The compression of the main frames 7 is then released, applying tension to the shadow mask 3.
Referring to FIGS. 2 and 3A, in a related art frame assembly, the shadow mask 3 is welded at ends 3a, 3b of the main frames 7-1 under tension. The frame assembly 7 with the shadow mask 3 attached thereto is then connected to the stud pins 18 on the panel 1 by springs 8 on an inside surface of the panel 1, to couple the frame assembly 7 with the panel 1.
To cope with howling, or a vibration of the shadow mask, in the related art, the main frames 7-1 are welded to the shadow mask 3 while the main frames 7-1 are compressed at a fixed load, as shown in FIG. 3B. The compression load is then released, putting the shadow mask under tension in a vertical direction, that is, in the direction of arrow A in FIGS. 1 and 3A. In this instance, the tension is configured to have a xe2x80x98Uxe2x80x99 shaped distribution, so as to cope with howling by setting a range of vibration for the different frequency bands of, for example, an external vibration source of a speaker in a TV receiver.
However, though the related art CRT provides a counter measure for addressing howling, that is, applying tension to the shadow mask in a vertical direction to increase a natural frequency of the shadow mask, the natural frequency of the shadow mask in such a frame assembly decreases as a vertical length height) of the shadow mask increases following an increase in the size of the TV receiver. When the natural frequency drops, the shadow mask assembly vibrates even at low frequency sound received from the speaker in the TV receiver sash, and thus becomes susceptible to howling.
Since the longer the shadow mask, the lower the natural frequency of the shadow mask for the same amount of tension, in order to apply optimal tension to the shadow mask in a frame assembly to prevent howling, the natural frequency must be increased to apply tension favorable to avoiding howling. To apply the required tension to the shadow mask, the compression applied to the frame must be increased so as to produce greater deformation.
In order to compress the frame to greater deformation, since the frame deformation must be within a range of elastic deformation where the frame comes back to an original position when the compression is released, a yielding stress of the frame must be enhanced by heat treating the frame or by changing the material of the frame.
The related art shadow mask has a problem that the vibration range is wide because there is almost no rigidity difference between a center part and the corner parts of the shadow mask. Further, there is not a great variation in natural frequencies between the center part and the corner parts of the shadow mask, even if the tension distribution is configured to have a xe2x80x98Uxe2x80x99 distribution in the related art frame assembly.
An object of the invention is to substantially solve at least one or more of the above problems and/or disadvantages in whole or in part and to provide at least the advantages described hereinafter.
Accordingly, the invention is directed to a shadow mask frame assembly in a CRT that substantially obviates at least one or more of the problems due to limitations and disadvantages of the related art.
Another object of the invention is to provide a shadow mask frame assembly in a CRT which can cope with a quality degradation of a center part of a shadow mask, the most susceptible part of the CRT to howling.
In order to achieve at least the above objects in whole or in part and in accordance with the purposes of the invention, as embodied and broadly described, a CRT according to the invention may include a panel having a fluorescent surface formed on an inside surface thereof, a tension type shadow mask fitted to the panel with a gap formed between the shadow mask and the panel, and a frame. The frame may include two main frames to which the tension type shadow mask is affixed under tension, and two subframes fixed to respective ends of the two main frames, wherein a distance between the two main frames increases from center part or portion of the main frames to an edge part or portion during assembly when the main frames are compressed, the tension type shadow mask is welded thereto, and the compression applied to the frames is released thereafter.
It is preferable that, when it is assumed that xe2x80x98axe2x80x99 denotes a distance between the main frames before compression, and xe2x80x98bxe2x80x99 denotes a distance between the main frames where the main frames are compressed and the shadow mask is welded thereto, a compression change ratio xe2x80x98Rcxe2x80x99 of the main frames at the center of the main frames satisfies the range expressed by equation (1) as follows:
3.0%xe2x89xa6Rc=(acxe2x88x92bc)/ac*100xe2x89xa65.0%xe2x80x83xe2x80x83(1)
And, at a position approximately 90% from the center part of the main frames, the compression change ratio R satisfies the following range expressed by equation (2) as follows:
0.90%xe2x89xa6R90%=(a90%xe2x88x92b90%)/a90%* 100xe2x89xa61.67%xe2x80x83xe2x80x83(2)
To further achieve at least the above objects in whole or in part and in accordance with the purposes of the invention, as embodied and broadly described, a CRT according to the invention may include a panel having a fluorescent surface, a shadow mask fitted to the panel with a gap formed therebetween, and a frame. The frame may include at least two main frames configured to be fixed to the shadow mask, and at least two subframes fixed respectively to ends of the main frames, wherein during assembly of the main frames and the shadow mask, the main frames are compressed such that a distance between the main frames at a center portion thereof is smaller than a distance between the main frames at an edge portion thereof.
To further achieve at least the above objects in whole or in part and in accordance with the purposes of the invention, as embodied and broadly described, a method of manufacturing a cathode ray tube comprising a panel having a fluorescent surface, a shadow mask fitted to the panel with a gap formed therebetween, and a frame including a pair of main frames and a pair of subframes fixed respectively to ends of the pair of subframes, according to the invention may include compressing the main frames such that a distance between the main frames at center portions of the main frames is smaller than a distance between the main frames at an edge portion of the main frames, welding the shadow mask to the main frames, and releasing the compression.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.